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Exposure to stress plays a detrimental role in the pathogenesis of hypertension via neuroinflammation pathways. Microglial neuroinflammation in the rostral ventrolateral medulla (RVLM) exacerbates stress-induced hypertension (SIH) by increasing sympathetic hyperactivity. Mitochondria of microglia are the regulators of innate immune response. Sigma-1R (σ-1R) localizes to the mitochondria-associated membranes (MAMs) and regulates endoplasmic reticulum (ER) and mitochondria communication, in part through its chaperone activity. The present study aims to investigate the protective role of σ-1R on microglial-mediated neuroinflammation. Stress-induced hypertension (SIH) was induced in rats using electric foot shocks and intermittent noise. Arterial blood pressure (ABP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were measured to evaluate the sympathetic nervous system (SNS) activities. SKF10047 (100 µM), an agonist of σ-1R, was administrated to rats, then σ-1R localization and MAM alterations were detected by immuno-electron microscopy. Mitochondrial calcium homeostasis was examined in primary microglia and/or BV-2 microglia cells. The effect of SKF10047 treatment on the mitochondrial respiratory function of cultured microglia was measured using a Seahorse Extracellular Flux Analyzer. Confocal microscopic images were performed to indicate mitochondrial dynamics. Stress reduces σ-1R's localization at the MAMs, leading to decreased ER-mitochondria contact and IP3R-GRP75-VDAC calcium transport complexes expression in the RVLM of rats. SKF10047 promotes the length and coverage of MAMs in the prorenin-treated microglia. Prorenin treatment increases mitoROS levels, and inhibits Ca 2+ signalling between the two organelles, therefore negatively affects ATP production in BV2 cells, and these effects are reversed by SKF10047 treatment. We found mitochondrial hyperfusion and microglial M1 polarization in prorenin-treated microglia. SKF10047 suppresses microglial M1 polarization and RVLM neuroinflammation, subsequently ameliorates sympathetic hyperactivity in stress-induced hypertensive rats. Sigma-1 receptor activation suppresses microglia M1 polarization and neuroinflammation via regulating endoplasmic reticulum-mitochondria contact and mitochondrial functions in stress-induced hypertension rats., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Mitochondria are essential for neuronal survival and function, and mitochondrial dysfunction plays a critical role in the pathological development of Parkinson's disease (PD). Mitochondrial quality control is known to contribute to the survival of dopaminergic (DA) neurons, with mitophagy being a key regulator of the quality control system. In this study, we show that mitophagy is impaired in the substantia nigra pars compacta (SNc) of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. Treatment with the sigma-1 receptor (Sig 1R) agonist 2-morpholin-4-ylethyl 1-phenylcyclohexane-1-carboxylate (PRE-084) reduced loss of DA neurons, restored motor ability and MPTP-induced damage to mitophagy activity in the SNc of PD-like mice. Additionally, knockdown of Sig 1R in SH-SY5Y DA cells inhibited mitophagy and enhanced 1-methyl-4-phenylpyridinium ion (MPP + ) neurotoxicity, whereas application of the Sig 1R selective agonist SKF10047 promoted clearance of damaged mitochondria. Moreover, knockdown of Sig 1R in SH-SY5Y cells resulted in decreased levels of p-ULK1 (Unc-51 Like Autophagy Activating Kinase 1) (Ser 555 ), p-TBK1 (TANK Binding Kinase 1) (Ser 172 ), p-ubiquitin (Ub) (Ser 65 ), Parkin recruitment, and stabilization of PTEN-induced putative kinase 1 (PINK1) in mitochondria. The present data provide the first evidence for potential roles of PINK1/Parkin in Sig 1R-modulated mitophagy in DA neurons., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Astrocyte is considered to be a type of passive supportive cells that preserves neuronal activity and survival. The dysfunction of astrocytes is involved in the pathological processes of major depression. Recent studies implicate sigma-1 receptors as putative therapeutic targets for current available antidepressant drugs. However, it is absent of direct evidences whether sigma-1 receptor could promote activation of astrocyte. In the present study, we took advantage of primary astrocyte culture and a highly selective agonist of sigma-1 receptor, (+)SKF-10047 to determine the effect of sigma-1 receptor on Brdu (bromodeoxyuridine) labeling positive cells, migration as well as GFAP (glial fibrillary acidic protein) expression of astrocyte. The results showed that (+)SKF-10047 notably increased the number of Brdu labeling positive cells, migration, and the expression of GFAP in primary astrocytes, which were blocked by antagonist of sigma-1 receptor. Moreover, we also found that (+)SKF-10047 increased the phosphorylation of ERK1/2 (extracellular signal-regulated kinases 1/2) and GSK3β (glycogen synthase kinase 3β) (ser 9) in the primary astrocytes. In addition, pharmacological inhibition of ERK1/2 and GSK3β (ser 9) abolished sigma-1 receptor-promoted activation of astrocyte. Therefore, sigma-1 receptor could be considerate as a new pattern for modulating astrocytic function might emerge as therapeutic strategies.

Expression of Kv1.2 within Kv1.x potassium channel complexes is critical in maintaining appropriate neuronal excitability and determining the threshold for action potential firing. This is attributed to the interaction of Kv1.2 with a hitherto unidentified protein that confers bimodal channel activation gating, allowing neurons to adapt to repetitive trains of stimulation and protecting against hyperexcitability. One potential protein candidate is the sigma-1 receptor (Sig-1R), which regulates other members of the Kv1.x channel family; however, the biophysical nature of the interaction between Sig-1R and Kv1.2 has not been elucidated. We hypothesized that Sig-1R may regulate Kv1.2 and may further act as the unidentified modulator of Kv1.2 activation. In transiently transfected HEK293 cells, we found that ligand activation of the Sig-1R modulates Kv1.2 current amplitude. More importantly, Sig-1R interacts with Kv1.2 in baseline conditions to influence bimodal activation gating. These effects are abolished in the presence of the auxiliary subunit Kvβ2 and when the Sig-1R mutation underlying ALS16 (Sig-1R-E102Q), is expressed. These data suggest that Kvβ2 occludes the interaction of Sig-1R with Kv1.2, and that E102 may be a residue critical for Sig-1R modulation of Kv1.2. The results of this investigation describe an important new role for Sig-1R in the regulation of neuronal excitability and introduce a novel mechanism of pathophysiology in Sig-1R dysfunction., (© 2019 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

The serotonin transporter (SERT) is functionally regulated via membrane trafficking. Our previous studies have demonstrated that the SERT C-terminal deletion mutant (SERTΔCT) showed a robust decrease in its membrane trafficking and was retained in the endoplasmic reticulum (ER), suggesting that SERTΔCT is an unfolded protein that may cause ER stress. The Sigma-1 receptor (SigR1) has been reported to attenuate ER stress via its chaperone activity. In this study, we investigated the effects of SKF-10047, a prototype SigR1 agonist, on the membrane trafficking and uptake activity of SERT and SERTΔCT expressed in COS-7 cells. Twenty-four hours of SKF-10047 treatment (>200 μM) accelerated SERT membrane trafficking and robustly upregulated SERTΔCT activity. Interestingly, these effects of SKF-10047 on SERT functions were also found in cells in which SigR1 expression was knocked down by shRNA, suggesting that SKF-10047 exerted these effects on SERT via a mechanism independent of SigR1. A cDNA array study identified several candidate genes involved in the mechanism of action of SKF-10047. Among them, Syntaxin3, a member of the SNARE complex, was significantly upregulated by 48 h of SKF-10047 treatment. These results suggest that SKF-10047 is a candidate for ER stress relief., (Copyright © 2018 The Authors. Production and hosting by Elsevier B.V. All rights reserved.)

Sigma receptor (σR), a unique receptor family, is classified into three subtypes: σR1, σR2 and σR3. It was previously shown that σR1 activation induced by 1μM SKF10047 (SKF) suppressed N-methyl-d-aspartate (NMDA) receptor-mediated responses of rat retinal ganglion cells (GCs) and the suppression was mediated by a distinct Ca(2+)-dependent phospholipase C (PLC)-protein kinase C (PKC) pathway. In the present work, using whole-cell patch-clamp techniques in rat retinal slice preparations, we further demonstrate that SKF of higher dosage (50μM) significantly suppressed AMPA receptor (AMPAR)-mediated light-evoked excitatory postsynaptic currents (L-EPSCs) of retinal ON-type GCs (ON GCs), and the effect was reversed by the σR1 antagonist BD1047, suggesting the involvement of σR1. The SKF (50μM) effect was unlikely due to a change in glutamate release from bipolar cells, as suggested by the unaltered paired-pulse ratio (PPR) of AMPAR-mediated EPSCs of ON GCs. SKF (50μM) did not change L-EPSCs of ON GCs when the G protein inhibitor GDP-β-S or the protein kinase G (PKG) inhibitor KT5823 was intracellularly infused. Calcium imaging further revealed that SKF (50μM) did not change intracellular calcium concentration in GCs and persisted to suppress L-EPSCs when intracellular calcium was chelated by BAPTA. The SKF (50μM) effect was intact when protein kinase A (PKA) and phosphatidylinostiol (PI)-PLC signaling pathways were both blocked. We conclude that the SKF (50μM) effect is Ca(2+)-independent, PKG-dependent, but not involving PKA, PI-PLC pathways., (Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.)

N-allylnormetazocine (NANM; SKF 10,047) is a benzomorphan opioid that produces psychotomimetic effects. (+)-NANM is the prototypical agonist for the sigma-1 (σ1) receptor, and there is a widespread belief that the hallucinogenic effects of NANM and other benzomorphan derivatives are mediated by interactions with σ1 sites. However, NANM is also an agonist at the κ opioid receptor (KOR) and binds to the PCP site located within the channel pore of the NMDA receptor, interactions that could potentially contribute to the effects of NANM. NMDA receptor antagonists such as phencyclidine (PCP) and ketamine are known to disrupt prepulse inhibition (PPI) of acoustic startle, a measure of sensorimotor gating, in rodents. We recently found that racemic NANM disrupts PPI in rats, but it is not clear whether the effect is mediated by blockade of the NMDA receptor, or alternatively whether interactions with KOR and σ1 receptors are involved. The present studies examined whether NANM and its stereoisomers alter PPI in C57BL/6J mice, and tested whether the effects on PPI are mediated by KOR or σ1 receptors. Racemic NANM produced a dose-dependent disruption of PPI (3-30mg/kg SC). (+)-NANM also disrupted PPI, whereas (-)-NANM was ineffective. Pretreatment with the selective KOR antagonist nor-binaltorphimine (10mg/kg SC) or the selective σ1 antagonist NE-100 (1mg/kg IP) failed to attenuate the reduction in PPI produced by racemic NANM. We also found that the selective KOR agonist (-)-U-50,488H (10-40mg/kg SC) had no effect on PPI. These findings confirm that NANM reduces sensorimotor gating in rodents, and indicate that the effect is mediated by interactions with the PCP receptor and not by activation of KOR or σ1 receptors. This observation is consistent with evidence indicating that the σ1 receptor is not linked to hallucinogenic or psychotomimetic effects., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Rationale: We previously reported that the fluvoxamine-induced increase in prefrontal dopamine levels is enhanced by adrenalectomy/castration (which results in circulating neurosteroid deficiency), via combined activation of serotonin1A (5-HT1A) and σ1 receptors. However, the mechanistic details of the interaction between 5-HT1A and σ1 receptors are unknown., Objectives: Because most neurosteroids have affinity for γ-aminobutyric acid (GABA)A receptors, in the present study, we examined the involvement of GABAA receptors in this process., Results: Adrenalectomy/castration decreased pentobarbital-induced sleeping time in mice, suggesting that it reduced GABAA receptor function. The GABAA receptor antagonist picrotoxin (1 mg/kg) enhanced the fluvoxamine-induced increase in prefrontal dopamine, but not noradrenaline or serotonin, levels in mice, suggesting that picrotoxin mimicked the effect of adrenalectomy/castration. Picrotoxin also potentiated the increase in prefrontal dopamine levels mediated by co-administration of the 5-HT1A receptor agonist osemozotan and the σ1 receptor agonist (+)-SKF-10,047, while it did not affect the co-administration-induced changes in noradrenaline and serotonin levels. Conversely, the GABAA receptor agonist diazepam (1 mg/kg) blocked the effect of adrenalectomy/castration on the fluvoxamine-induced increase in prefrontal dopamine levels. Co-administration of osemozotan and (+)-SKF-10,047 did not affect the expression of the neuronal activity marker c-Fos in the prefrontal cortex, ventral tegmental area, and nucleus accumbens in control mice, while it increased the c-Fos expression only in the prefrontal cortex and ventral tegmental area in picrotoxin-treated mice., Conclusions: These results suggest that the GABAA receptor plays a key role in mediating the synergistic effects of 5-HT1A and σ1 receptor activation on prefrontal dopamine neurotransmission.

Aims: Sigma-1 receptors are involved in the pathophysiological process of several neuropsychiatric diseases such as epilepsy, depression. Allosteric modulation represents an important mechanism for receptor functional regulation. In this study, we examined antidepressant activity of the latest identified novel and selective allosteric modulator of sigma-1 receptor 3-methyl-phenyl-2, 3, 4, 5-tetrahydro-1H-benzo[d]azepin-7-ol (SOMCL-668)., Methods and Results: A single administration of SOMCL-668 decreased the immobility time in the forced swimming test (FST) and tailing suspended test in mice, which were abolished by pretreatment of sigma-1 receptor antagonist BD1047. In the chronic unpredicted mild stress (CUMS) model, chronic application of SOMCL-668 rapidly ameliorated anhedonia-like behavior (within a week), accompanying with the enhanced expression of brain-derived neurotrophic factor (BDNF) and phosphorylation of glycogen synthase kinase 3β (GSK3β) (Ser-9) in the hippocampus. SOMCL-668 also rapidly promoted the phosphorylation of GSK3β (Ser-9) in an allosteric manner in vitro. In the cultured primary neurons, SOMCL-668 enhanced the sigma-1 receptor agonist-induced neurite outgrowth and the secretion of BDNF., Conclusion: SOMCL-668, a novel allosteric modulator of sigma-1 receptors, elicits a potent and rapid acting antidepressant effect. The present data provide the first evidence that allosteric modulation of sigma-1 receptors may represent a new approach for antidepressant drug discovery., (© 2016 John Wiley & Sons Ltd.)

Sigma-1 receptors (σ-1Rs) are endoplasmic reticulum resident chaperone proteins implicated in many physiological and pathological processes in the CNS. A striking feature of σ-1Rs is their ability to interact and modulate a large number of voltage- and ligand-gated ion channels at the plasma membrane. We have reported previously that agonists for σ-1Rs potentiate NMDA receptor (NMDAR) currents, although the mechanism by which this occurs is still unclear. In this study, we show that in vivo administration of the selective σ-1R agonists (+)-SKF 10,047 [2S-(2α,6α,11R*]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol hydrochloride (N-allylnormetazocine) hydrochloride], PRE-084 (2-morpholin-4-ylethyl 1-phenylcyclohexane-1-carboxylate hydrochloride), and (+)-pentazocine increases the expression of GluN2A and GluN2B subunits, as well as postsynaptic density protein 95 in the rat hippocampus. We also demonstrate that σ-1R activation leads to an increased interaction between GluN2 subunits and σ-1Rs and mediates trafficking of NMDARs to the cell surface. These results suggest that σ-1R may play an important role in NMDAR-mediated functions, such as learning and memory. It also opens new avenues for additional studies into a multitude of pathological conditions in which NMDARs are involved, including schizophrenia, dementia, and stroke., (Copyright © 2014 the authors 0270-6474/14/3411325-14$15.00/0.)

Serotonin (5-HT)1A and σ1 receptors have been implicated in psychiatric disorders. We previously found that combined 5-HT reuptake inhibition and σ1 receptor activation has a synergistic effect on prefrontal dopaminergic transmission in adrenalectomized/castrated mice lacking circulating steroid hormones. In the present study, we examined the mechanisms underlying this neurochemical synergism. Systemic administration of fluvoxamine, a selective 5-HT reuptake inhibitor with agonistic activity towards the σ1 receptor, increased prefrontal dopamine (DA) levels, and adrenalectomy/castration potentiated this fluvoxamine-induced increase in DA. This enhancement of DA release was blocked by WAY100635 (a 5-HT1A receptor antagonist), but not by ritanserin (a 5-HT2 receptor antagonist), azasetron (a 5-HT3 receptor antagonist) or SB269970 (a 5-HT7 receptor antagonist). Individually, osemozotan (a 5-HT1A receptor agonist) and (+)-SKF-10,047 (a σ1 receptor agonist) did not alter prefrontal monoamine levels in adrenalectomized/castrated and sham-operated mice differentially. In contrast, co-administration of these drugs increased prefrontal DA levels to a greater extent in adrenalectomized/castrated mice than in sham-operated animals. Furthermore, co-administration of osemozotan and (+)-SKF-10,047 increased expression of the neuronal activity marker c-Fos in the ventral tegmental area of adrenalectomized/castrated mice, but not in sham-operated animals. These findings suggest that combined activation of 5-HT1A and σ1 receptors has a synergistic effect on prefrontal dopaminergic transmission under circulating steroid deficiency, and that this interaction may play an important role in the regulation of the prefrontal DA system., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

We used conscious tethered Sprague-Dawley rats to evaluate the cardiovascular effects of four sigma-1 (σ1 ) agonists and five antagonists, given alone or in combination. All drugs were administered as a single intraperitoneal dose. The agonists were given at doses reported as efficacious in rodent cognition models, while the antagonists were administered at doses neutralizing agonist effects in vivo. Systolic blood pressure (SBP) and heart rate (HR) were continuously recorded for 20 min before and 60 min postadministration. Immediately after injection, a sudden, transitory increase in HR and SBP was noted in all animals, because of the stress induced by handling. For both parameters, a peak value (ΔHRmax and ΔSBPmax ) and an area under the curve of changes from baseline over the period 5-20 min postinjection (ΔHR_AUC5-20 min and ΔSBP_AUC5-20 min ) were calculated. Three of the four σ1 agonists (SKF-10,047, dehydroepiandrosterone (DHEAS), Compound 14) significantly reduced ΔHR_AUC5-20 min value without changing ΔHRmax , while the fourth one, SA-4503, had no significant effect. None of the antagonists (haloperidol, rimcazole, NE-100, and BD1047) reduced, and even one (progesterone) enhanced the stress-induced effects on HR. No changes in SBP were noted with any compound. When the antagonist NE-100 was administered just before SKF-10,047, it completely reversed the inhibitory effects of the σ1 agonist on HR increase. In conclusion, we demonstrated for the first time the involvement of σ1 receptors in the regulation of handling-induced tachycardia in the conscious rat. Although additional investigations are needed to fully understand this role, it might offer new therapeutic perspectives to σ1 ligands in the cardiovascular sphere., (© 2012 The Authors Fundamental and Clinical Pharmacology © 2012 Société Française de Pharmacologie et de Thérapeutique. Published by John Wiley & Sons Ltd.)

Sigma-1 receptors (σ-1rs) exert neuroprotective effects on retinal ganglion cells (RGCs) both in vivo and in vitro. This receptor has unique properties through its actions on several voltage-gated and ligand-gated channels. The purpose of this study was to investigate the role that σ-1rs play in regulating cell calcium dynamics through activated L-type Voltage Gated Calcium Channels (L-type VGCCs) in purified RGCs. RGCs were isolated from P3-P7 Sprague-Dawley rats and purified by sequential immunopanning using a Thy1.1 antibody. Calcium imaging was used to measure changes in intracellular calcium after depolarizing the cells with potassium chloride (KCl) in the presence or absence of two σ-1r agonists [(+)-SKF10047 and (+)-Pentazocine], one σ-1r antagonist (BD1047), and one L-type VGCC antagonist (Verapamil). Finally, co-localization studies were completed to assess the proximity of σ-1r with L-type VGCCs in purified RGCs. VGCCs were activated using KCl (20 mM). Pre-treatment with a known L-type VGCC blocker demonstrated a 57% decrease of calcium ion influx through activated VGCCs. Calcium imaging results also demonstrated that σ-1r agonists, (+)-N-allylnormetazocine hydrochloride [(+)-SKF10047] and (+)-Pentazocine, inhibited calcium ion influx through activated VGCCs. Antagonist treatment using BD1047 demonstrated a potentiation of calcium ion influx through activated VGCCs and abolished all inhibitory effects of the σ-1r agonists on VGCCs, implying that these ligands were acting through the σ-1r. An L-type VGCC blocker (Verapamil) also inhibited KCl activated VGCCs and when combined with the σ-1r agonists there was not a further decline in calcium entry suggesting similar mechanisms. Lastly, co-localization studies demonstrated that σ-1rs and L-type VGCCs are co-localized in purified RGCs. Taken together, these results indicated that σ-1r agonists can inhibit KCl induced calcium ion influx through activated L-type VGCCs in purified RGCs. This is the first report of attenuation of L-type VGCC signaling through the activation of σ-1rs in purified RGCs. The ability of σ-1rs to co-localize with L-type VGCCs in purified RGCs implied that these two proteins are in close proximity to each other and that such interactions regulate L-type VGCCs., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Straub tail reaction (STR) was observed in male ddY mice after simultaneous administration with BMY 14802 (a non-specific σ receptor antagonist) and methamphetamine (METH). The intensity and duration of STR depended on the dose of BMY 14802. The tail reaction was inhibited completely by (+)-SKF 10,047 (a putative σ(1) receptor agonist) and partially by PB 28 (a putative σ(2) receptor agonist). The STR was mimicked in mice treated with BD 1047 (a putative σ(1) receptor antagonist), but not SM-21, a putative σ(2) receptor antagonist, in combination with METH. STR evoked with BD 1047 plus METH was inhibited by (+)-SKF 10,047. STR induced by BMY 14802 and METH was abolished by naloxone (a relatively non-selective opioid receptor antagonist) or U-50,488H (a selective κ-agonist), suggesting that the STR may be mediated by activation of opioid receptor system., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Treatment with sigma1 receptor (Sigma1) ligands can inhibit cell proliferation in vitro and tumor growth in vivo. However, the cellular pathways engaged in response to Sigma1 ligand treatment that contribute to these outcomes remain largely undefined. Here, we show that treatment with putative antagonists of Sigma1 decreases cell mass. This effect corresponds with repressed cap-dependent translation initiation in multiple breast and prostate cancer cell lines. Sigma1 antagonist treatment suppresses phosphorylation of translational regulator proteins p70S6K, S6, and 4E-BP1. RNAi-mediated knockdown of Sigma1 also results in translational repression, consistent with the effects of antagonist treatment. Sigma1 antagonist mediated translational repression and decreased cell size are both reversible. Together, these data reveal a role for Sigma1 in tumor cell protein synthesis, and demonstrate that small molecule Sigma1 ligands can be used as modulators of protein translation., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The present study was undertaken to identify possible similarities between the effects of kappa-opioid receptor agonist, N-methyl-D-aspartate-receptor antagonist, and sigma receptor agonist on the discriminative stimulus effects of U-50488H, and the possible involvement of sigma receptors in the discriminative stimulus and aversive effects of U-50488H. The kappa-opioid receptor agonist U-50488H produced significant place aversion as measured by the conditioned place preference procedure, and this effect was completely abolished by treatment with the putative sigma-1 receptor antagonist NE-100. In addition, phencyclidine (+)-SKF-10047 and (+)-pentazocine, which are sigma receptor agonists, generalized to the discriminative stimulus effects of U-50488H in rats that had been trained to discriminate between U-50488H (3.0 mg/kg) and saline. Furthermore, NE-100 significantly attenuated the discriminative stimulus effects of U-50488H and the U-50488H-like discriminative stimulus effects of phencyclidine. These results suggest that the sigma-1 receptor is responsible for both the discriminative stimulus effects and aversive effects of U-50488H., (© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction.)

σ-1 Receptors are expressed in the brain, and their activation has been shown to prevent neuronal death associated with glutamate toxicity. This study investigates the possible mechanism and effect of [2S-(2α,6α,11R*]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol (SKF10047), a σ-1 receptor agonist, on endogenous glutamate release in the nerve terminals of rat cerebral cortex. Results show that SKF10047 inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP), and the σ-1 receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047) blocked this phenomenon. The effects of SKF10047 on the evoked glutamate release were prevented by the chelating extracellular Ca²⁺ions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-β-benzyl-oxyaspartate did not have any effect on the action of SKF10047. SKF10047 decreased the depolarization-induced increase in the cytosolic free Ca²⁺ concentration ([Ca²⁺](C)), but did not alter 4-AP-mediated depolarization. Furthermore, the effects of SKF10047 on evoked glutamate release were prevented by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking the ryanodine receptors or the mitochondrial Na⁺/Ca²⁺ exchange. In addition, conventional protein kinase C (PKC) inhibitors abolished the SKF10047 effect on 4-AP-evoked glutamate release. Western blot analyses showed that SKF10047 decreased the 4-AP-induced phosphorylation of PKC and PKCα. These results show that σ-1 receptor activation inhibits glutamate release from rat cortical nerve terminals. This effect is linked to a decrease in [Ca²⁺](C) caused by Ca²⁺ entry through presynaptic voltage-dependent Ca²⁺ channels and the suppression of the PKC signaling cascade.

Recently, sigma-1 receptor modulators have been considered drugs with an interesting therapeutic potential for the treatment of anxiety. However, there is no clear information in preclinical studies about the possible effects of sigma-1 ligands on anxiety in experimental animal models. Therefore, the present study examined the effects of (+)SKF 10,047 (2-8 mg/kg, ip), a sigma-1 agonist, on anxiety, tested in two classical laboratory models (social interaction test and elevated plus maze). (+)SKF 10,047 (8 mg/kg) produced a significant decrease of social investigation in the "social interaction test", whereas in the "elevated plus maze", the drug (4 and 8 mg/kg) provoked a significant reduction in the number of entries into open arms, as well as in the time spent in this area, as compared with the control group, without affecting motor activity. Overall, these findings indicate that (+)SKF 10,047 exhibits an anxiogenic-like profile in mice. It is suggested that anxiogenic effects of this sigma-1 ligand could be related to its potent ability to modulate diverse neurotransmitter systems involved in anxiety regulation.

(+)-SKF 10047 (N-allyl-normetazocine) is a prototypic and specific sigma-1 receptor agonist that has been used extensively to study the function of sigma-1 receptors. (+)-SKF 10047 inhibits K(+), Na(+) and Ca2+ channels via sigma-1 receptor activation. We found that (+)-SKF 10047 inhibited Na(V)1.2 and Na(V)1.4 channels independently of sigma-1 receptor activation. (+)-SKF 10047 equally inhibited Na(V)1.2/1.4 channel currents in HEK293T cells with abundant sigma-1 receptor expression and in COS-7 cells, which barely express sigma-1 receptors. The sigma-1 receptor antagonists BD 1063,BD 1047 and NE-100 did not block the inhibitory effects of (+)-SKF-10047. Blocking of the PKA, PKC and G-protein pathways did not affect (+)-SKF 10047 inhibition of Na(V)1.2 channel currents. The sigma-1 receptor agonists Dextromethorphan (DM) and 1,3-di-o-tolyl-guanidine (DTG) also inhibited Na(V)1.2 currents through a sigma-1 receptor-independent pathway. The (+)-SKF 10047 inhibition of Na(V)1.2 currents was use- and frequency-dependent. Point mutations demonstrated the importance of Phe(1764) and Tyr(1771) in the IV-segment 6 domain of the Na(V)1.2 channel and Phe(1579) in the Na(V)1.4 channel for (+)-SKF 10047 inhibition. In conclusion, our results suggest that sigma-1 receptor agonists directly inhibit Na(V)1.2/1.4 channels and that these interactions should be given special attention for future sigma-1 receptor function studies.

Rationale: Fluvoxamine, a selective serotonin (5-HT) reuptake inhibitor (SSRI) and an agonist for the σ(1) receptors, increases extracellular monoamines in the prefrontal cortex, but it is not known whether the σ(1) receptor is involved in the neurochemical effect of fluvoxamine., Objectives: In view of the fact that circulating steroids exert a tonic modulatory effect on σ(1) receptor-mediated effects, the present study examines the effects of fluvoxamine on prefrontal extracellular monoamine levels in adrenalectomized/castrated mice lacking the peripheral sources of steroids., Results: Fluvoxamine-induced increases in the extracellular levels of dopamine (DA), but not of 5-HT and noradrenaline, were significantly higher in adrenalectomized/castrated than in sham-operated mice, and this effect was blocked by BD1047, a selective σ(1) receptor antagonist. In contrast, the effects of paroxetine, an SSRI without affinity for the σ(1) receptors, and (+)-SKF-10,047, a selective σ(1) receptor agonist, on the extracellular monoamine levels did not differ between adrenalectomized/castrated and sham-operated mice, while the increase in extracellular DA levels induced by co-administration of these drugs was higher in adrenalectomized/castrated than in the control mice. Moreover, fluvoxamine increased c-Fos expression, a marker of neuronal activity, in the prefrontal cortex of adrenalectomized/castrated mice, and this effect was blocked by BD1047. The similar increase in c-Fos expression was observed by co-administration of paroxetine and (+)-SKF-10,047., Conclusions: These findings suggest that fluvoxamine enhances prefrontal dopaminergic neurotransmission via both 5-HT reuptake inhibition and σ(1) receptor activation under the circulating neuroactive steroid-deficient conditions.

σ-Receptors are integral membrane proteins that have been implicated in a number of biological functions, many of which involve the modulation of ion channels. A wide range of synthetic ligands activate σ-receptors, but endogenous σ-receptor ligands have proven elusive. One endogenous ligand, dimethyltryptamine (DMT), has been shown to act as a σ-receptor agonist. Progesterone and other steroids bind σ-receptors, but the functional consequences of these interactions are unclear. Here we investigated progesterone binding to σ(1)- and σ(2)-receptors and evaluated its effect on σ-receptor-mediated modulation of voltage-gated Na(+) channels. Progesterone binds both σ-receptor subtypes in liver membranes with comparable affinities and blocks photolabeling of both subtypes in human embryonic kidney 293 cells that stably express the human cardiac Na(+) channel Na(v)1.5. Patch-clamp recording in this cell line tested Na(+) current modulation by the σ-receptor ligands ditolylguanidine, PB28, (+)SKF10047, and DMT. Progesterone inhibited the action of these ligands to varying degrees, and some of these actions were reduced by σ(1)-receptor knockdown with small interfering RNA. Progesterone inhibition of channel modulation by drugs was consistent with stronger antagonism of σ(2)-receptors. By contrast, progesterone inhibition of channel modulation by DMT was consistent with stronger antagonism of σ(1)-receptors. Progesterone binding to σ-receptors blocks σ-receptor-mediated modulation of a voltage-gated ion channel, and this novel membrane action of progesterone may be relevant to changes in brain and cardiovascular function during endocrine transitions.

We previously demonstrated that intracerebroventricular (i.c.v.) administration of the substance P (SP) aminoterminal fragment SP(1-7) attenuates the expression of morphine withdrawal in the male rat. In this study we have used a synthetic analogue of this peptide, i.e. the SP(1-7) amide showing higher binding potency than the native heptapeptide, in a similar experimental set-up. Thus, Wistar male rats were made tolerant to morphine by daily injections of the opiate during 8 days. Following peptide administration (i.c.v.) and a subsequent naloxone challenge a variety of physical syndromes of withdrawal were recorded. We observed that the SP(1-7) amide potently and dose-dependently reduced several signs of reaction to morphine withdrawal. Interestingly, the effect of the peptide amide was significantly attenuated by the addition of the sigma agonist (+)-SKF-10047. We conclude that the SP(1-7) amide mimics the effect of the native SP fragment and that the mechanisms for its action involve a sigma receptor site.

Objective: The effects of sigma receptor antagonists on methamphetamine (METH)-induced stereotypy have not been examined. We examined the effects of sigma antagonists on METH-induced stereotypy in mice., Results: The administration of METH (10 mg/kg) to male ddY mice induced stereotyped behavior consisting of biting (90.1%), sniffing (4.2%), head bobbing (4.1%), and circling (1.7%) during an observation period of 1 h. Pretreatment of the mice with BMY 14802 (alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazinebutanol; 1, 5, and 10 mg/kg), a non-specific sigma receptor antagonist, significantly increased METH-induced sniffing (19.2%, 30.5%, and 43.8% of total stereotypical behavior) but decreased biting (76.6%, 66.9%, and 49.3% of total stereotypical behavior) in a dose-dependent manner. This response was completely abolished by (+)-SKF 10,047 ([2S-(2alpha,6alpha,11R)]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol; 4 and 10 mg/kg), a putative sigma(1) receptor agonist, and partially by PB 28 (1-cyclohexyl-4-[3-(1,2,3,4-tetrahydro-5-methoxy-1-naphthalen-1-yl)-n-propyl]piperazine; 1 and 10 mg/kg), a putative sigma(2) receptor agonist. The BMY 14802 action on METH-induced stereotypy was mimicked by BD 1047 (N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine; 10 mg/kg), a putative sigma(1) receptor antagonist, but not by SM-21 ((+/-)-tropanyl 2-(4-chlorophenoxy)butanoate; 1 mg/kg), a putative sigma(2) receptor antagonist. The BD 1047 effect on METH-induced stereotypy was also abolished completely by (+)-SKF 10,047 and partially by PB 28. The overall frequency of METH-induced stereotypical behavior was unchanged with these sigma receptor ligands, despite the alteration in particular behavioral patterns. The BMY 14802 action on METH-induced stereotypy was unaffected by pretreatment with centrally acting histamine H(1) receptor antagonists (pyrilamine or ketotifen, 10 mg/kg), suggesting that these effects are independent of histamine H(1) receptor signaling systems., Conclusion: In summary, modulation of central sigma(1) receptors alters the pattern of METH-induced stereotypy, producing a shift from stereotypical biting to stereotypical sniffing, without affecting the overall frequency of stereotypical behavior.

The sigma-receptor, a broadly distributed integral membrane protein with a novel structure, is known to modulate various voltage-gated K(+) and Ca(2+) channels through a mechanism that involves neither G proteins nor phosphorylation. The present study investigated the modulation of the heart voltage-gated Na(+) channel (Na(v)1.5) by sigma-receptors. The sigma(1)-receptor ligands [SKF-10047 and (+)-pentazocine] and sigma(1)/sigma(2)-receptor ligands (haloperidol and ditolylguanidine) all reversibly inhibited Na(v)1.5 channels to varying degrees in human embryonic kidney 293 (HEK-293) cells and COS-7 cells, but the sigma(1)-receptor ligands were less effective in COS-7 cells. The same four ligands also inhibited Na(+) current in neonatal mouse cardiac myocytes. In sigma(1)-receptor knockout myocytes, the sigma(1)-receptor-specific ligands were far less effective in modulating Na(+) current, but the sigma(1)/sigma(2)-receptor ligands modulated Na(+) channels as well as in wild type. Photolabeling with the sigma(1)-receptor photoprobe [(125)I]-iodoazidococaine demonstrated that sigma(1)-receptors were abundant in heart and HEK-293 cells, but scarce in COS-7 cells. This difference was consistent with the greater efficacy of sigma(1)-receptor-specific ligands in HEK-293 cells than in COS-7 cells. sigma-Receptors modulated Na(+) channels despite the omission of GTP and ATP from the patch pipette solution. sigma-Receptor-mediated inhibition of Na(+) current had little if any voltage dependence and produced no change in channel kinetics. Na(+) channels represent a new addition to the large number of voltage-gated ion channels modulated by sigma-receptors. The modulation of Na(v)1.5 channels by sigma-receptors in the heart suggests an important pathway by which drugs can alter cardiac excitability and rhythmicity.

Purpose: The sigma-1 receptor belongs to a recently discovered family of transmembrane proteins expressed in the central nervous system, including the eye, and mediates the regulation of ion channels. The exact function of sigma receptors remains to be elucidated. The purpose of this study was to investigate the effect of sigma-1 receptor ligands on calcium homeostasis in a retinal ganglion cell line (RGC)-5 and rat primary RGCs., Methods: Calcium imaging was used to assess the effect of sigma-1 receptor agonist (+)-N-allylnormetazocine ((+)-SKF10047) on potassium chloride (KCl)-induced calcium influx in RGC-5. The whole-cell patch clamp technique was used to analyze the effect of (+)-SKF10047 on calcium currents in primary RGCs. Coimmunoprecipitation assessed the interaction between the sigma-1 receptor and the L-type voltage-gated calcium channel., Results: The sigma-1 receptor agonist (+)-SKF10047 inhibited potassium chloride (KCl)-induced calcium influx. The sigma-1 receptor antagonist, BD1047, reversed the inhibitory effect of (+)-SKF10047. Whole-cell patch clamp recordings of rat cultured primary RGCs demonstrated that (+)-SKF10047 inhibited calcium currents. Coimmunoprecipitation studies demonstrated an association between L-type calcium channels and the sigma-1 receptors., Conclusions: These results suggest that sigma-1 receptor activation can regulate calcium homeostasis and signaling in RGCs, likely by directly influencing the activity of L-type voltage-gated calcium channels. Regulation of calcium influx in RGCs by sigma-1 receptor ligands may represent in part the neuroprotective effect of sigma-1 receptors.

Purpose: sigma-1 Receptor ligands prevent neuronal death associated with glutamate excitotoxicity both in vitro and in vivo. However, the molecular mechanism of the neuroprotective effect remains to be elucidated. The present study was undertaken to determine whether sigma-1 receptor agonists provide neuroprotection by decreasing glutamate-induced calcium mobilization and preventing apoptotic gene expression., Methods: Cell death was measured by using a calcein-AM/propidium iodide cell-survival assay. Western blot analysis determined the expression levels of Bax in normal RGC-5 cells. Caspase-3 activation after glutamate treatment was determined with a carboxyfluorescein caspase-3 detection kit. Glutamate-induced intracellular calcium mobilization was measured by using ratiometric calcium imaging., Results: sigma-1 Receptor-overexpressing RGC-5 (RGC-5-S1R) cells had lower glutamate-induced intracellular calcium mobilization than did normal RGC-5 cells, and the sigma-1 receptor ligand (+)-SKF10047 reduced the glutamate calcium response in normal and RGC-5-S1R cells. (+)-SKF10047 protected RGC-5 cells from glutamate-induced cell death, and the RGC-5-S1R cells showed a significant resistance to glutamate-induced apoptosis compared with the control RGC-5 cells. BD1047, a sigma-1 receptor antagonist, blocked the protective effect of (+)-SKF10047. Western blot analysis showed that (+)-SKF10047 inhibited the increase in Bax after glutamate treatments. Glutamate-mediated cell death involved activation of caspase-3, and sigma-1 receptor activation prevented an increase in caspase-3 expression., Conclusions: The results suggest that sigma-1 receptors regulate intracellular calcium levels and prevent activation of proapoptotic genes, thus promoting retinal ganglion cell survival. The sigma-1 ligands appear to be neuroprotective and are a potential target for neuroprotective therapeutics.

We conducted virtual docking studies using GLIDE with modified LXRbeta ligand-binding domain (LBD) on internal compound collection followed by the gene profiling with ArrayPlate mRNA assay. A total of 69 compounds were found to upregulate LXRalpha and certain LXR regulated genes from 1308 compounds selected by virtual screen (hit rate: 5.3%). Compound 4 was shown to significantly induce the expression of LXR target genes such as ABCA1, ABCG1, APOE, SCD-1, and SREBP-1c in THP-1 differentiated macrophages. In vitro binding assay confirmed that 4 binds to both LXRalpha and LXRbeta directly and recruits coactivator peptide SRC-1. It functions as a full LXR agonist in stimulating cholesterol efflux in THP-1 differentiated macrophages and induces lipogenesis in HepG2 cells. This study demonstrates that the combination of virtual screen and high throughput gene profiling is an efficient approach for rapid identification of novel LXR modulators.

Lipid rafts are membrane platforms that spatially organize molecules for specific signaling pathways that regulate various cellular functions. Cholesterol is critical for liquid-ordered raft formation by serving as a spacer between the hydrocarbon chains of sphingolipids, and alterations in the cholesterol contents of the plasma membrane causes disruption of rafts. The role that sigma receptors play in cancer is not clear, although it is frequently up-regulated in human cancer cells and tissues and sigma receptors inhibit proliferation in carcinoma and melanoma cell lines, induce apoptosis in colon and mammary carcinoma cell lines, and reduce cellular adhesion in mammary carcinoma cell lines. In this study, we provide molecular and functional evidence for the involvement of the enigmatic sigma 1 receptors in lipid raft modeling by sigma 1 receptor-mediated cholesterol alteration of lipid rafts in breast cancer cell lines. Cholesterol binds to cholesterol recognition domains in the COOH terminus of the sigma 1 receptor. This binding is blocked by sigma receptor drugs because the cholesterol-binding domains form part of the sigma receptor drug-binding site, mutations of which abolish cholesterol binding. Furthermore, we outline a hypothetical functional model to explain the myriad of biological processes, including cancer, in which these mysterious receptors are involved. The findings of this study provide a biological basis for the potential therapeutic applications of lipid raft cholesterol regulation in cancer therapy using sigma receptor drugs.

Using whole-cell voltage-clamp recordings, hyperpolarization-activated cation currents (Ih) were elicited with hyperpolarizing voltage jumps in CA1 pyramidal neurons of rat hippocampal slices, and the effects of phencyclidine (PCP) and some sigma ligands on Ih were studied. PCP concentration-dependently (0.1-100 microM) suppressed Ih and shifted the activation curve of Ih to the negative direction. D-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, 20 microM) and MK-801 (30 microM), competitive and non-competitive NMDA blockers, respectively, failed to mimic the inhibitory effect of PCP on Ih, and suppression of Ih by PCP was unaffected in the presence of these blockers. To explore the involvement of sigma1 receptors in the reduction of Ih, the effects of representative sigma1 ligands were studied. SKF10047 (100 microM), a sigma1 agonist, attenuated the maximal Ih and shifted the half-activation potential of Ih to the hyperpolarized direction. In the presence of the sigma1 antagonist NE-100 (1 microM), which alone did not affect Ih, the effect of SKF10047 on Ih was unaltered. By contrast, a higher concentration of NE-100 (10 microM) mimicked the effect of SKF10047. Again, no antagonism of Ih suppression by SKF10047 was obtained with rimcazole (100 microM), a sigma1 receptor antagonist that is structurally distinct from NE-100. This concentration of rimcazole alone resulted in a slight but significant reduction of Ih. Thus these major sigma1 ligands appear to suppress Ih independently of their agonistic or antagonistic properties. The results of this study suggest that PCP and some sigma ligands could modulate cell excitability partly through their action on Ih.

The sigma(2)-receptor agonist, ifenprodil, was suggested as an inhibitor of G protein-coupled inwardly rectifying potassium channels. Nevertheless, an analysis of the role of sigma(2) receptors in cardiac electrophysiology has never been done. This work aims i) to identify the roles of cardiac sigma(2) receptors in the regulation of cardiac K(+) channel conductances and ii) to check whether sigma(2)-receptor agonists exhibit class III antiarrhythmic properties. The sigma(2)-receptor agonists ifenprodil, threo-ifenprodil, LNP250A [threo-8-[1-(4-hydroxyphenyl)-1-hydroxy-propan-2-yl]-1-phenyl-1,3,8-triazaspiro[4,5]decane-4-one] (a derivative of ifenprodil devoid of alpha(1)-adrenergic and N-methyl-d-aspartate glutamate receptor-blocking properties), and 1,3-di(2-tolyl)guanidine were used to discriminate the effects linked to sigma(2) receptors from those of the sigma(1) subtype, induced by (+/-)-N-allylnormetazocine (SKF-10,047). The sigma(2)-receptor antagonist 3-alpha-tropanyl-2(pCl-phenoxy)butyrate (SM-21) was employed to characterize sigma(2)-mediated effects in patch-clamp experiments. In rabbits, all sigma(2)-receptor agonists reduced phenylephrine-induced cardiac arrhythmias. They prolonged action potential duration in rabbit Purkinje fibers and reduced human ether-a-go-go-related gene (HERG) K(+) currents. (+)-SKF-10,047 was completely inactive in the last two tests. The effects of threo-ifenprodil were not antagonized by SM-21. In HERG-transfected COS-7 cells, SM-21 potentiated the ifenprodil-induced blockade of the HERG current. These data suggest that sigma(2)-receptor ligands block I(Kr) and that this effect could explain part of the antiarrhythmic properties of this ligands family. Nevertheless, an interaction with HERG channels not involving sigma(2) receptors seems to share this pharmacological property. This work shows for the first time that particular caution has to be taken toward ligands with affinity for sigma(2) receptors. The repolarization prolongation and the early-afterdepolarization can be responsible for "torsades de pointe" and sudden cardiac death.

In the present study, we examined the involvement of the sigma1 receptor in the inhibitory effect of the selective serotonin reuptake inhibitor (SSRI) fluvoxamine, compared with that of paroxetine, on marble-burying behavior, which is an animal model of obsessive-compulsive disorder. Sigma1 receptor agonists (+)-SKF 10047 and PRE-084 significantly inhibited marble-burying behavior. Sigma receptor antagonist BD 1047 and selective sigma1 receptor antagonist BD 1063 significantly attenuated the inhibition of marble-burying behavior by fluvoxamine. In contrast, selective sigma2 receptor antagonist SM-21 failed to affect the inhibition of marble-burying behavior by fluvoxamine. On the other hand, BD 1047 and BD 1063 had no effect on the inhibition of marble-burying behavior by paroxetine. These observations show that activation of the sigma1 receptor is a necessary component in the inhibitory effect of fluvoxamine on marble-burying behavior, and that the mechanism of its action is clearly different from that of paroxetine.

sigma-1 Receptors have been identified in numerous brain regions, including areas such as hypothalamus and amygdala, which have long been linked to the regulation of aggression. However, there is no clear information with respect to the possible effects of sigma-1 ligands on aggressive behavior in laboratory animals. Consequently, the present study examined the effects of (+)SKF 10047 (0.5-6 mg/kg, i.p.), a sigma-1 prototypical agonist, on isolation-induced aggression in male mice, using an ethopharmacological approach. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration. Ten minutes of diadic interactions were staged between a singly housed and an anosmic mouse in a neutral area. The encounters were videotaped, and the accumulated time allocated by subjects to 10 broad behavioral categories was estimated using an ethologically based analysis. Results showed that (+)SKF 10047 (6 mg/kg) produced a significant reduction of offensive behaviors, without affecting immobility. Social investigation behaviors were also slightly increased after drug treatment (2-6 mg/kg). These results suggest a role for sigma-1 receptors in aggression modulation in mice.

We evaluated the effects of phenytoin (DPH) on the affinity for sigma-1 (sigma(1)) receptors of agonist or antagonist sigma(1) ligands in guinea pig brain. Heterologous competition experiments showed that DPH (250 microM and 1 mM) concentration-dependently increased the affinity of the sigma(1) agonists dextromethorphan, (+)-SKF-10,047, (+)-3-PPP, and PRE-084. However, neither DPH 250 microM nor 1 mM increased (in fact, they slightly decreased) the affinity of the sigma(1) receptor antagonists haloperidol, BD 1063, NE-100, progesterone, and BD 1047. These findings suggest that allosteric modulation by DPH of the affinity of sigma(1) receptor ligands depends on the agonist or antagonist characteristics of the ligand. Therefore, determining in vitro the differential modulation by DPH of sigma(1) ligand affinity appears to constitute a procedure that can predict the pharmacological profile of different sigma(1) ligands.

The sigma1 receptor is a unique intracellular receptor whose activation results in an efficient modulation of several neurotransmitter responses. Its role as a target for the rapid nongenomic effects of neuro(active)steroids and the age-related diminutions in steroid levels suggested that targeting the sigma1 receptor might allow alleviation of age-related neuronal dysfunctions. We examined here the expression and behavioral efficacy of sigma1 receptors in the senescence-accelerated (SAM) mouse model. The sigma1 receptor mRNA expression was measured by using comparative RT-PCR in the olfactory bulb, hippocampus, hypothalamus, cortex, or cerebellum of senescence-prone SAMP/8 and senescence-resistant SAMR/1 control animals. No difference was observed between substrains in 6-, 9-, and 12-month-old (m.o.) mice. The sigma1 protein expression was analyzed by using immunohistochemical techniques. Labeling was intense in the olfactory bulb, hippocampus, hypothalamus, and midbrain of both SAMR/1 and SAMP/8 mice, and the distribution appeared unchanged in 6-, 9-, and 12-m.o. animals. The receptor's in vivo availability was examined by using in vivo [3H](+)-SKF-10,047 binding. No age-related difference was observed in the olfactory bulb, hippocampus, hypothalamus, cortex, cerebellum, and brainstem of 6- or 12-m.o. SAMR/1 or SAMP/8 mice. The antidepressant efficacy of the selective agonist igmesine was examined in the forced-swimming test. The compound decreased significantly the immobility duration at 60 mg/kg in 6- and 12-m.o. SAMR/1 and in 6-m.o. SAMP/8 mice. In 12-m.o. SAMP/8 mice, the drug efficacy was facilitated; a significant effect was measured at 30 mg/kg. Decreased neurosteroid levels, particularly of progesterone, were seen in 12-m.o. SAMP/8 mice that might explain the enhanced efficacy of igmesine. Preserved sigma1 receptor expression and enhanced behavioral efficacy of sigma1 agonists were measured in SAM animals, confirming the therapeutic opportunities for selective ligands against age-related mood disorders., (Copyright (c) 2005 Wiley-Liss, Inc.)

The ability of non-competitive NMDA antagonists and other selected compounds to inhibit [3H]MK-801 binding to the NMDA receptor in brain membranes was evaluated in female, dark Agouti rats. In homologous competition binding studies the average apparent affinity (KD) of [3H]MK-801 for its binding site was 5.5 nM and the binding site density (Bmax) was 1.83 pmol/mg protein. Inhibition of [3H]MK-801 binding by non-competitive NMDA antagonists was best described with a one-site competition model and the average Hill coefficients were -1. A series of eight non-competitive NMDA antagonists inhibited [3H]MK-801 binding with the following rank order of affinity (K(i), nM): MK-801 (5.5) > dexoxadrol (21.5) > or = TCP (24.2) > phencyclidine (100.8) > (+)-SKF 10,047 (357.7) > dextrorphan (405.2) > ketamine (922.2) > dextromethorphan (2913). These inhibition binding constants determined in dark Agouti rat brain membranes were significantly correlated (P = 0.0002; r2 = 0.95) with previously reported values determined in Sprague-Dawley rats [Wong et al., 1988, J. Neurochem. 50, 274-281]. Despite significant differences in metabolic capability between these strains, the central nervous system NMDA receptor ion channel shares similar characteristics., (Copyright 2004 Elsevier Inc.)

Our previous study reported that an antitussive drug, dimemorfan, attenuates cholinergic dysfunction-induced amnesia in mice and acts like a sigma1 receptor agonist. This study further showed that dimemorfan (30 microM), like the putative sigma1 receptor agonist (+)-SKF-10047 (10 microM), significantly enhanced 25 mM KCl-evoked [3H]acetylcholine release from rat hippocampal but not striatal slices, which was antagonized by a sigma1 receptor antagonist haloperidol (0.3 microM).

Pharmacological effects of amantadine on dopaminergic transmission are proposed to result from an uncompetitive antagonism at glutamate N-methyl-D-aspartate (NMDA) receptors. However, our previous studies examining amantadine-mediated dopamine receptor regulation in the rat striatum revealed a discrepancy from a direct interference with glutamate transmission. Preliminary in vitro binding data from the literature suggested the interaction of amantadine with the sigma1 receptor. Therefore, we have now further characterized the pharmacological properties of amantadine and memantine at this receptor and investigated its involvement in the modulation of striatal dopaminergic transmission. Our binding studies using [3H]-(+)SKF-10,047 indicated that amantadine and memantine behave as ligands of the sigma(1) receptor in rat forebrain homogenates (Ki values of 7.44 +/- 0.82 and 2.60 +/- 0.62 microm, respectively). In NG108-15 neuroblastoma cells, both drugs (amantadine (100 microm) and memantine (10 microm)) potentiated the bradykinin-induced mobilization of intracellular Ca2+, mimicking the effect of the sigma1 receptor agonist PRE-084 (1 microm). Finally, we previously showed that in striatal membranes from amantadine-treated rats, the functional coupling of dopamine receptors with G-proteins was enhanced. Similarly, PRE-084 dose-dependently increased the [35S]GTPgammaS binding induced by dopamine (Emax 28 and 26% of basal, 0.3 and 1 mg/kg PRE-084, respectively). By contrast, BD1047, which is without effect on its own, antagonized the effects of amantadine and PRE-084. Together, these data demonstrate that aminoadamantanes behave as sigma1 receptor agonists, and confirm an involvement of this receptor in modulating dopamine receptors exerted by therapeutically relevant concentrations of amantadine.

In vivo or in vitro administration of a omega 1 receptor agonist d-SKF 10,047 (1 mg/kg intravenously or 10 mg/l in vitro) promoted an increase in the resistance of isolated perfused rat heart to ischemia/reperfusion injury. Both in vivo and in vitro stimulation of omega receptors prevents development of reperfusion contracture and release of creatine kinase and increases the developed pressure, double product, +dP/dt, and -dP/dt in the left ventricle. Activation of omega receptors has no significant effect on the occurrence of reperfusion arrhythmias ex vivo. Stimulation of cardiac sigma receptors is proposed to prevent myocardial stunning.

Treatment of depressive symptoms in patients suffering from neurodegenerative disorders remains a challenging issue, since few available antidepressants present an adequate efficacy during pathological aging. Previous reports suggested that selective sigma(1) receptor agonists might constitute putative candidates. We here examined the pharmacological efficacy of igmesine and (+)-SKF-10,047 and the sigma(1) receptor-related neuroactive steroid dehydroepiandrosterone sulfate, in rats infused intracerebroventricularly during 14 days with the beta-amyloid-(1-40) protein and then submitted to the conditioned fear stress test. Igmesine and (+)-SKF-10,047 significantly reduced the stress-induced motor suppression at 30 and 6 mg/kg, respectively, in beta-amyloid-(40-1)-treated control rats. Active doses were decreased, to 10 and 3 mg/kg, respectively, in beta-amyloid-(1-40)-treated animals. The dehydroepiandrosterone sulfate effect was also facilitated, both in dose (10 vs. 30 mg/kg) and intensity, in beta-amyloid-(1-40)-treated rats. Neurosteroid levels were measured in several brain structures after beta-amyloid infusion, in basal and stress conditions. Progesterone levels, both under basal and stress-induced conditions, were decreased in the hippocampus and cortex of beta-amyloid-(1-40)-treated rats. The levels in pregnenolone, dehydroepiandrosterone and their sulfate esters appeared less affected by the beta-amyloid infusion. The sigma(1) receptor agonist efficacy is known to be inversely correlated to brain progesterone levels, synthesized mainly by neurons that are mainly affected by the beta-amyloid toxicity. The present study suggests that sigma(1) receptor agonists, due to their enhanced efficacy in a nontransgenic animal model, may alleviate Alzheimer's disease-associated depressive symptoms.

In this study we aimed to (1). screen phenothiazines for cytotoxic activity in glioma, neuroblastoma, and primary mouse brain tissue; and (2). determine the mechanism of the cytotoxic effect (apoptosis, necrosis) and the roles of calmodulin inhibition and sigma receptor modulation. Rat glioma (C6) and human neuroblastoma (SHSY-5Y) cell lines were treated with different phenothiazines. All agents induced a dose-dependent decrease in viability and proliferation, with the highest activity elicited by thioridazine. Sensitivity to thioridazine of glioma and neuroblastoma cells was significantly higher (p < 0.05) than that of primary mouse brain culture (IC50 11.2 and 15.1 microM vs 41.3 microM, respectively). The N-mustard fluphenazine induced significantly lower cytotoxicity in glioma cells, compared to fluphenazine. The sigma receptor selective ligand (+)-SK&F10047 increased viability slightly while combined with fluphenazine; SK&F10047 did not alter fluphenazine activity. Flow cytometry of propidium iodide (PI)-stained glioma cells treated with thioridazine, fluphenazine, or perphenazine (6-50 microM) resulted in a concentration-dependent increase of fragmented DNA up to 94% vs 3% in controls by all agents. Thioridazine (12.5 microM)-treated glioma cells costained with PI and Hoechst 33342 revealed a red fluorescence of fragmented nuclei in treated cells and a blue fluorescence of intact control nuclei. After 4-h exposure to thioridazine (25 and 50 microM), a 25- to 30-fold increase in caspase-3 activity in neuroblastoma cells was noted. Overall, the marked apoptotic effect of phenothiazines in brain-derived cancer cells, and the low sensitivity of primary brain tissue suggest the potential use of selected agents as therapeutic modalities in brain cancer.

1. Current antitussive medications have limited efficacy and often contain the opiate-like agent dextromethorphan (DEX). The mechanism whereby DEX inhibits cough is ill defined. DEX displays affinity at both NMDA and sigma receptors, suggesting that the antitussive activity may involve central or peripheral activity at either of these receptors. This study examined and compared the antitussive activity of DEX and various putative sigma receptor agonists in the guinea-pig citric-acid cough model. 2. Intraperitoneal (i.p.) administration of DEX (30 mg kg(-1)) and the sigma-1 agonists SKF-10,047 (1-5 mg kg(-1)), Pre-084 (5 mg kg(-1)), and carbetapentane (1-5 mg kg(-1)) inhibited citric-acid-induced cough in guinea-pigs. Intraperitoneal administration of a sigma-1 antagonist, BD 1047 (1-5 mg kg(-1)), reversed the inhibition of cough elicited by SKF-10,047. In addition, two structurally dissimilar sigma agonists SKF-10,047 (1 mg ml(-1)) and Pre-084 (1 mg ml(-1)) inhibited cough when administered by aerosol. 3. Aerosolized BD 1047 (1 mg ml(-1), 30 min) prevented the antitussive action of SKF-10,047 (5 mg kg(-1)) or DEX (30 mg kg(-1)) given by i.p. administration and, likewise, i.p. administration of BD 1047 (5 mg kg(-1)) prevented the antitussive action of SKF-10,047 given by aerosol (1 mg ml(-1)). 4. These results therefore support the argument that antitussive effects of DEX may be mediated via sigma receptors, since both systemic and aerosol administration of sigma-1 receptor agonists inhibit citric-acid-induced cough in guinea-pigs. While significant systemic exposure is possible with aerosol administration, the very low doses administered (estimated <0.3 mg kg(-1)) suggest that there may be a peripheral component to the antitussive effect.

Sigma (sigma) sites are a type of nonopiate receptor whose role has been associated with several behaviours, including anxiety, depression, analgesia, learning processes and psychosis. Although there are several known sigma receptor types, only the type I receptor (sigma 1) has been cloned. To uncover the in vivo relevance of sigma-receptors, we have generated knockout mice for sigma 1. Despite the broad expression pattern found for the sigma 1-gene, homozygous mutant mice are viable, fertile and do not display any overt phenotype, compared with their wild-type litter-mates, in mixed genetic backgrounds. However, a significant decrease in the hypermotility response has been measured in knockout mice upon challenge with (+)SKF-10 047, in agreement with the involvement of sigma 1-receptors in the induction of psychostimulant actions. The activity of sigma 2-receptors seems to be unaffected in sigma 1-mutant mice. These knockout mice could contribute to better understand the in vivo role of sigma-receptors.

(1) Dimemorfan, an antitussive for more than 25 years, has previously been reported to be a relative high-affinity ligand at sigma-1 (sigma(1)) receptor with the K(i) value of 151 nM. (2) To test whether dimemorfan has anti-amnesic effects similar to a sigma(1) receptor agonist, this study examined its effects on scopolamine- and beta-amyloid peptide-(25-35)-induced amnesia in mice. (3) Dimemorfan (10-40 mg kg(-1), i.p.) administered 30 min before the training trial, immediately after the training trial, or 30 min before the retention test significantly improved scopolamine (1 mg kg(-1), i.p.)- or beta-amyloid peptide-(25-35) (3 nmol mouse(-1), i.c.v.)-induced amnesia in a step-through passive avoidance test. Dimemorfan (5-40 mg kg(-1), i.p.) pretreatment also attenuated scopolamine (8 mg kg(-1), i.p.)-induced amnesia in a water-maze test. And, these anti-amnesic effects of dimemorfan, like the putative sigma(1) receptor agonist (+)-N-allylnormetazocine ((+)-SKF-10047), were antagonized by a sigma receptor antagonist haloperidol (0.25 mg kg(-1), i.p.). (4) These results indicated that dimemorfan has anti-amnesic effects and acts like a sigma(1) receptor agonist.

Background: The aim of the present study was to describe the activity of a set of opioid drugs, including partial agonists, in a cell system expressing only mu opioid receptors. Receptor activation was assessed by measuring the inhibition of forskolin-stimulated cyclic adenosine mono phosphate (cAMP) production. Efficacies and potencies of these ligands were determined relative to the endogenous ligand beta-endorphin and the common mu agonist, morphine., Results: Among the ligands studied naltrexone, WIN 44,441 and SKF 10047, were classified as antagonists, while the remaining ligands were agonists. Agonist efficacy was assessed by determining the extent of inhibition of forskolin-stimulated cAMP production. The rank order of efficacy of the agonists was fentanyl = hydromorphone = beta-endorphin > etorphine = lofentanil = butorphanol = morphine = nalbuphine = nalorphine > cyclazocine = dezocine = metazocine >or= xorphanol. The rank order of potency of these ligands was different from that of their efficacies; etorphine > hydromorphone > dezocine > xorphanol = nalorphine = butorphanol = lofentanil > metazocine > nalbuphine > cyclazocine > fentanyl > morphine >>>> beta-endorphin., Conclusion: These results elucidate the relative activities of a set of opioid ligands at mu opioid receptor and can serve as the initial step in a systematic study leading to understanding of the mode of action of opioid ligands at this receptor. Furthermore, these results can assist in understanding the physiological effect of many opioid ligands acting through mu opioid receptors.

We investigated the effects of sigma receptor ligands on neuronal death induced by chemical ischemia using primary cultures of rat cerebral cortical neurons. The induction of chemical ischemia by sodium azide and 2-deoxy-D-glucose led to delayed neuronal death in a time- and concentration-dependent manner, as determined by trypan blue exclusion. The neurotoxicity was inhibited by N-methyl-D-aspartate (NMDA) receptor antagonists, indicating the involvement of glutamate. The sigma receptor ligands (+)-N-allylnormetazocine ((+)-SKF10,047) and haloperidol, but not carbetapentane and R(+)-3-(3-hydroxyphenyl)-N-propylpiperidine ((+)-3-PPP), prevented chemical ischemia-induced neurotoxicity in a concentration-dependent manner. The protective effects of (+)-SKF10,047 and haloperidol were not affected by the sigma receptor antagonists. (+)-SKF10,047 and haloperidol, but not carbetapentane and (+)-3PPP, inhibited the glutamate-induced increase in intracellular Ca(2+), and the inhibitory effects were not attenuated by sigma receptor antagonists. These results suggest that direct interaction with NMDA receptors but not sigma receptors is crucial to the neuroprotective effects of sigma receptor ligands with affinity for NMDA receptors., (Copyright 2002 Elsevier Science B.V.)

(R)-(+)-1-(4-Chlorophenyl)-3-[4-(2-methoxyethyl)piperazin-1-yl]methyl-2-pyrrolidinone L-tartrate (MS-377) is a novel antipsychotic agent with selective and high affinity for sigma(1) receptor. The present study was carried out to clarify the interaction of MS-377 with dopamine D(2) receptor antagonists (D(2) antagonists) in concurrent administration, and then the involvement of sigma receptors in the interaction. The effects of MS-377 on haloperidol- or sultopride-induced inhibition of apomorphine-induced climbing behavior and catalepsy were investigated in mice and rats, respectively. In addition, the effects of (+)-SKF-10,047 and SA4503, both of which are sigma receptor agonists, and WAY-100,635, which is a 5-HT(1A) receptor antagonist, on the interaction due to the concurrent use were also investigated. MS-377 potentiated the inhibitory effects of haloperidol or sultopride on apomorphine-induced climbing behavior in a dose-dependent manner. In contrast, MS-377 did not affect the catalepsy induction by these drugs. The potentiation of the inhibitory effects of haloperidol or sultopride on apomorphine-induced climbing behavior by MS-377 was not inhibited by WAY-100,635, but was inhibited by (+)-SKF-10,047 and SA4503. These findings showed that MS-377 potentiates the efficacy of D(2) antagonists, but it does not deteriorate the adverse effect. Moreover, sigma(1) receptors are involved in this potentiation of the efficacy of D(2) antagonists by MS-377.

The sigma(1) (sigma(1)) receptor exerts a potent neuromodulatory role in the brain with relevant consequences in memory processes, response to stress, depression and pharmacodependence. Its precise endogenous ligand is not yet identified but the sigma(1) receptor appears to be one target for the nongenomic rapid effects of neuroactive steroids in the brain. The aim of the present study was to establish whether differences in sigma(1) receptor-mediated behaviours could be observed among mouse strains, in relation with differences in either sigma(1) receptor expression or steroid levels. The sigma(1)-receptor immunohistochemical distribution appeared similar between Swiss and C57BL/6 strains in all the brain structures examined. The levels of in vivo [(3)H](+)-SKF-10 047 binding to sigma(1) receptors were lower in Swiss than in C57BL/6. Adrenalectomy/castration significantly increased [(3)H](+)-SKF-10 047 binding only in Swiss. The behavioural efficacy of the selective sigma( 1) agonists igmesine and PRE-084 -- reversion of the scopolamine-induced amnesia in the passive avoidance test; diminution of the immobility duration in the forced swimming test -- were significantly higher in C57BL/6 than in Swiss. Steroid levels were measured in the brain in basal conditions and after stress. C57BL/6 mice presented in both conditions, the lowest progesterone levels, this steroid acting as an endogenous sigma(1) antagonist. Collectively, the results suggested that strain differences in neuroactive steroid and particularly, progesterone, biosynthesis and sensitivity may contribute to the differential behavioural efficacy of sigma(1)-receptor ligands. Noteworthy, these observations are coherent with strain differences observed in the intensity of cocaine-induced reward properties, known to critically involve the sigma(1) receptor.

The sigma receptor is a novel protein that mediates the modulation of ion channels by psychotropic drugs through a unique transduction mechanism depending neither on G proteins nor protein phosphorylation. The present study investigated sigma receptor signal transduction by reconstituting responses in Xenopus oocytes. Sigma receptors modulated voltage-gated K+ channels (Kv1.4 or Kv1.5) in different ways in the presence and absence of ligands. Association between Kv1.4 channels and sigma receptors was demonstrated by coimmunoprecipitation. These results indicate a novel mechanism of signal transduction dependent on protein-protein interactions. Domain accessibility experiments suggested a structure for the sigma receptor with two cytoplasmic termini and two membrane-spanning segments. The ligand-independent effects on channels suggest that sigma receptors serve as auxiliary subunits to voltage-gated K+ channels with distinct functional interactions, depending on the presence or absence of ligand.

MS-377 ((R)-(+)-1-(4-chlorophenyl)-3-[4-(2-methoxyethyl)piperazin-1-yl]methyl-2-pyrrolidinone L-tartrate) is a antipsychotic agent that binds to sigma-1 receptor. MS-377 showed anti-dopaminergic and anti-serotonergic activities and antagonistic action against phencyclidine (PCP)-induced behaviors in an animal model. These anti-psychotic activities of MS-377 are attributable to association with sigma-1 receptor. However, the mechanism by which the sigma-1 receptor ligands exact those numerous effects remains to be elucidated. In the present study, we evaluated the effect of MS-377 on N-methyl-D-aspartate (NMDA) receptor ion-channel complex in primary cultured rat neuronal cells. First, we examined the effect of MS-377 on NMDA-induced Ca2+ influx with fura-2/ AM loaded cells. MS-377 showed no effects on the basal Ca2+ concentration and NMDA-induced Ca2+ influx by itself PCP and SKF-10047 reduced the NMDA-induced increase in intracellular Ca2+ concentration. Pre-incubation of 1 microM MS-377 was found to significantly block the reduction by PCP or SKF-10047 of the NMDA-induced Ca2+ influx. Second, the effect of MS-377 on [3H]MK-801 intact cell binding was examined. PCP, haloperidol and (+)-pentazocine inhibited [3H]MK-801 binding, although MS-377 showed no effect by itself Pre-treatment of MS-377 markedly reversed the inhibition of [3H]MK-801 binding by PCP in a dose-dependent manner. These effects of MS-377 may depend on its affinity for the sigma-1 receptor, because MS-377 is a selective sigma-1 receptor ligand without any affinity for NMDA receptor ion-channel complex. These observations suggest that the MS-377 indirectly modulated the NMDA receptor ion-channel complex, and the anti-psychotic activities of MS-377, in part, are attributable to such on action via sigma-1 receptor.

NMDA glutamate receptor antagonists are used in clinical anesthesia, and are being developed as therapeutic agents for preventing neurodegeneration in stroke, epilepsy, and brain trauma. However, the ability of these agents to produce neurotoxicity in adult rats and psychosis in adult humans compromises their clinical usefulness. In addition, an NMDA receptor hypofunction (NRHypo) state might play a role in neurodegenerative and psychotic disorders, like Alzheimer's disease and schizophrenia. Thus, understanding the mechanism underlying NRHypo-induced neurotoxicity and psychosis could have significant clinically relevant benefits. NRHypo neurotoxicity can be prevented by several classes of agents (e.g. antimuscarinics, non-NMDA glutamate antagonists, and alpha(2) adrenergic agonists) suggesting that the mechanism of neurotoxicity is complex. In the present study a series of experiments was undertaken to more definitively define the receptors and complex neural circuitry underlying NRHypo neurotoxicity. Injection of either the muscarinic antagonist scopolamine or the non-NMDA antagonist NBQX directly into the cortex prevented NRHypo neurotoxicity. Clonidine, an alpha(2) adrenergic agonist, protected against the neurotoxicity when injected into the basal forebrain. The combined injection of muscarinic and non-NMDA Glu agonists reproduced the neurotoxic reaction. Based on these and other results, we conclude that the mechanism is indirect, and involves a complex network disturbance, whereby blockade of NMDA receptors on inhibitory neurons in multiple subcortical brain regions, disinhibits glutamatergic and cholinergic projections to the cerebral cortex. Simultaneous excitotoxic stimulation of muscarinic (m(3)) and glutamate (AMPA/kainate) receptors on cerebrocortical neurons appears to be the proximal mechanism by which the neurotoxic and psychotomimetic effects of NRHypo are mediated.